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Known differences between SimH, 11/70, and w11a

SimH: SPL doesn't have 11/70 behavior

On an 11/70, the SPL instruction in the 11/70 always fetches the next instruction regardless of current mode, pending device, or even console interrupts. This behavior is used in some xxdp diagnostic codes to prepare a situation suitable for interrupt response testing.

SimH does not implement this behavior, SPL behaves like all other instructions, and interrupts or traps are honored after it completes. xxdp ekbbf0 test 32 depends on the 11/70 behavior and is skipped.

The w11 implements 11/70 behavior for SPL in kernel mode only. In supervisor or user mode SPL is a nop and honors traps and interrupts, see SPL on w11.